Nowadays, wireless HDMI transmitting devices usually require a power adapter to supply power, which takes too much space of the wireless HDMI transmitting device and a socket interface is needed to connect with a plug of the power adapter. Thus, it is inconvenient to use. In addition, in order to save electrical energy, when the wireless HDMI transmitting device is not in use, users need to remove the wireless HDMI transmitting device from a signal source, and turn off the power adapter or unplug the plug of the power adapter, which is inconvenient.